1. Field of the Invention
The present invention relates to a manufacturing method of an absorbent article including a first web which constitutes a front waistband part, and a second web which constitutes a rear waistband part.
2. Description of the Related Art
Generally, an absorbent article, such as a disposable diaper, includes: a front waistband part which corresponds to a front portion around the waistline of a wearer; a rear waistband part which corresponds to a rear portion around the waistline of the wearer; a crotch part which corresponds to the crotch of the wearer; and leg openings which open at sides of the crotch part.
The front waistband part and the rear waistband part are bonded to each other from an upper edge portion of the absorbent article from which a waistline portion of the wearer is to be inserted (i.e., an edge portion corresponding to a waist portion of the wearer) to each leg opening. These portions where the front and rear waistband parts are bonded to each other (hereinafter, referred to as bonded part) are each formed of a waist portion including a waist gather, a leg portion including a leg gather, and a fit portion located between the waist gather and the leg gather.
A manufacturing method of such an absorbent article includes a step of bonding predetermined regions of the first web which constitutes the front waistband part and the second web which constitutes the rear waistband part which are in a overlapped state, the predetermined regions provided to the first web and the second web with a predetermined interval in a conveyance direction of the first web and the second web, and each corresponding to a bonded part.
For example, there is known a technique of bonding a first web and a second web by outputting ultrasonic vibration to a predetermined region using an ultrasonic bonding device (for example, see Japanese Patent Application Publication No. Hei 5-15551 (pages 2 and 3, and FIG. 4)). The ultrasonic bonding device includes an anvil roll which supports the first web and the second web, and an ultrasonic mechanism which faces the anvil roll and which outputs the ultrasonic vibration to the predetermined region between itself and the anvil roll.
Specifically, the ultrasonic mechanism includes an ultrasonic vibrator (oscillator) which generates ultrasonic vibration, and an ultrasonic horn (vibrator) which outputs the ultrasonic vibration generated by the ultrasonic vibrator to the predetermined region. The ultrasonic horn includes an input surface for receiving the ultrasonic vibration generated by the ultrasonic vibrator, and an output surface for outputting the ultrasonic vibration inputted to the input surface to the predetermined region. Note that, in order to output the ultrasonic vibration to the predetermined region as equally as possible, the ultrasonic vibrator and the vibrator are connected in an input center region corresponding to an output center region, the input center region including the center of the input surface, the output center region including the center of the output surface.
However, the aforementioned conventional technique has the following problems. Specifically, since the ultrasonic vibrator is connected to the ultrasonic horn in the input center region, the ultrasonic vibration having inputted to the input surface from the ultrasonic vibrator is outputted in a manner of decreasing from the output center region corresponding to the input center region with distance from the output center region. In other words, the output of the ultrasonic vibration decreases with distance from the output center region.
This makes the bonding strength of the first web and the second web in a region corresponding to each fit portion stronger than the bonding strength of the first web and the second web in a region corresponding to each waist portion, as well as than the bonding strength of the first web and the second web in a region corresponding to each leg portion.
Therefore, when a wearer puts on and off an absorbent article (at the time of putting on and off), the waist portion and the leg portions can be separated easily, which consequently reduces the durability of the absorbent article. Further, if the waist portion can be separated easily, the absorbent article is less likely to fit the waist portion of the wearer while the wearer wears the absorbent article (while being worn). Meanwhile, if the leg portions can be separated easily, the absorbent article is less likely to fit around the legs of the wearer while being worn. Accordingly, excrement from the wearer may leak from the absorbent article (a so-called leakage prevention capability may be deteriorated).
Conceivable methods for addressing the above problems include strongly bonding the whole predetermined region (that is, increasing the entire bonding strength). However, if the bonding strength of the whole predetermined region is increased, it becomes difficult to tear the bonded part (a so-called disassembling property is deteriorated) when the wearer disposes the absorbent article (at the time of disposal).
As described above, in addition to basic properties originally needed, such as the improvement of the durability of the absorbent article at the time of putting on and off and the leakage prevention capability while being worn, it is required for the absorbent article to have additional properties contradictory to the basic properties, such as the disassembling property required when the wearer disposes the absorbent article (at the time of disposal).